The present invention relates to a method for providing temporary coloration to a polyamide textile fiber, with a heat degradable poly(oxyalkylene) substituted methine colorant.
Fugitive colorants which have achieved wide acceptance in the textile industry include the poly(oxyethylene) substituted colorants described in U.S. Pat. No. 3,517,633. These colorants or tints are used to identify fiber types by color coding undyed fiber during the textile manufacturing process and to enhance the visibility of the fibers. After the fiber is made into a textile product, for example after having been tufted into a substrate to make carpeting, the fugitive colorant is removed by scouring with an aqueous solution. These colorants are a combination of a dyestuff radical and one or more poly(oxyethylene) groups. Suitable dyestuff radicals disclosed in the patent include nitroso, nitro, azo, diphenylmethane, triarylmethane, xanthene, acridine, methine, thiazole, indamine, azine, oxazine and anthraquinone radicals. The dyestuff radical may be attached to the poly(oxyethylene) group by an amino nitrogen.
Normally, the fugitive colorants are applied to the fiber prior to heat setting. Textile fibers, especially thermoplastics such as nylon and polyester, are heat set during processing to provide bulk and texture to yarns made from the fibers. For example, in the Suessen process, nylon 6 continuous filament or staple fibers are dry heatset at 190.degree. C. to 195.degree. C. for 40 to 90 seconds. One of the advantages of the aforementioned poly(oxyethylene) substituted colorants is that they may generally be removed by scouring, even after such heat setting conditions.
The removal of fugitive colorants from fibers has become increasingly difficult with the development of wet heat setting processes which employ superheated steam, such as in the Superba process. It is believed that moisture from the saturated steam disrupts the hydrogen bonding network in the polyamide fiber, thereby lowering the softening temperature and increasing the crystallization rate of the polymer. Polyamide fiber, and in particular nylon 6 fiber, tends to swell slightly in high humidity and temperature, which allows penetration of the colorant into interstices in the fiber. Consequently, even colorants which are highly water soluble become bound to the fiber upon cooling and cannot be readily removed with traditional scouring techniques.
Also, with the advent of improved carpet dyeing techniques, such as the Kuster Dyer, scouring of the carpet with copious quantities of water is becoming unnecessary and, in fact, may be undesirable except for the necessity of removing the fugitive colorant. Furthermore, while conventional fugitive colorants have in the past generally been applied at levels below about 0.5% of colorant based upon the weight of the fiber, increasing tint levels are being used to maintain proper identification of fibers during processing. When conventional fugitive colorants are used at such higher levels, for example above about 0.5 wt % removal of all of the colorant may become increasingly difficult.
Poly(oxyalkylene) substituted methine colorants have been previously employed to color polyester materials, to color liquids containing nonionic surfactants and in washable ink compositions, as disclosed in the following United States patents. In Rekers, U.S. Pat. No. 4,758,243 a solution of a methine colorant is applied to a polyester fabric and the fabric is heated in a forced air oven at 190.degree. to 210.degree. C. for fifteen minutes. The colorant was found to penetrate into the polyester material. Aqueous and non-aqueous liquids containing a nonionic surfactant and a methine colorant are shown in U.S. Pat. No. 4,871,371. Suggested liquid compositions include cosmetics, inks, paper products, cleaning solutions, detergents, herbicides, gasoline, antifreeze, paint, plastics, and in the textile industry Finally, Kluger et al., U.S. Pat. No. 4,981,516 disclose washable ink compositions containing poly(oxyalkylene) substituted methine colorants.
All of the above identified United States patents are incorporated by reference.